Apparatus for counterbalancing weight

ABSTRACT

The invention relates to an apparatus for counterbalancing the weight of movable machine parts of a machine tool. A simply and compactly designed apparatus of this kind enabling a weight compensation even without complex pressure means supplies is, according to the invention, characterized in that it comprises one or more helical springs ( 1; 15  to  18 ) the one end ( 7; 29 ) of which is connected to a stationary component ( 8; 19 ) and the other end ( 2; 31 ) of which is connected to the movable machine part ( 12; 35 ) for generating a counter-force counteracting the weight force of the movable machine part ( 12; 35 ).

[0001] The invention relates to an apparatus for counterbalancing theweight of movable machine components of a machine tool.

[0002] In the field of machine tools the weight of the verticallymovable machine parts is often counterbalanced by counterweights todecrease the driving power during lifting operations as well as toincrease the acceleration, said counterweights being connected to themovable machine parts such as, for example, milling units, consoles ortransverse beams via roller chains or ropes. Particularly in machinetools of compact construction, however, there is no space for suchcounterweights and the additionally required guidances.

[0003] Therefore, a hydraulic or hydro-pneumatic weight counterbalanceis also used already in which the weight of a vertically shiftablemachine part is compensated by one or more pressure cylinders. However,corresponding means for the pressure means supply and control membersfor adjusting and maintaining the pressure in the pressure cylinders arerequired in this type of weight compensation.

[0004] It is the object of the invention to provide an apparatus of thetype mentioned at the beginning which is simple and compact in designand will also enable weight compensation without complex pressure meanssupplies and control means.

[0005] According to the invention said object is solved in that theapparatus comprises one or more helical springs one end of which isconnected to a stationary component and the other end of which isconnected to the movable machine part to generate a counter-forcecounteracting the weight force of the movable machine part.

[0006] With the apparatus according to the invention particularly theweight force of vertically or obliquely movable machine parts may betotally or partially counter1 balanced with simple means. In this waythe driving power required for lifting the machine parts can be reduced.The feeding drive is less strained even when larger masses are lifted,and greater accelerations are obtainable.

[0007] Efficacious embodiments and advantageous forms of the inventionare indicated in the subclaims.

[0008] Thus, the apparatus comprises a plurality of parallelly connectedhelical springs in a particularly efficacious embodiment, said helicalsprings being disposed between the machine part to be moved and astationary component. With a plurality of helical springs the springcharacteristic may be optimally adjusted to the prevailing requirements.In addition, safety is provided for the case that a fracture or the likeoccurs in one of the helical springs.

[0009] In an embodiment sealed towards the outside to a large extent theinner end of the helical springs is attached to an axis and the outerend to a housing concentric with respect to the axis. The axis may bearranged so as to be stationary, and the housing may be formed so as tobe turnable. However, the housing may as well be designed so as to bestationary, and the axis may be formed so as to be rotatable.

[0010] In an embodiment with a fixed axis and a movable housing thelatter is advantageously connected to the machine part to be moved via agear belt capable of enduring great loads which will be wound up on theefficaciously drum shaped central part of the housing when the machinepart is lifted. However, other pulling elements may also be used forconnecting the housing with the shiftable machine part.

[0011] According to another efficacious embodiment the helical springsdisposed adjacent to each other are separated from each other by spacerdisks. In this way an undesired friction between the individual springsmay be prevented.

[0012] For biasing the helical springs a corresponding adjustment flangemay be provided on the axis which flange can be turned via radial boresand fixed on an angular console or another stationary machine part in adesired angular position via front side fixing screws or the like.

[0013] Other particularities and advantages of the invention will becomeobvious from the following description of advantageous embodiments withreference to the drawings in which:

[0014]FIG. 1 is a considerably simplified schematic illustration of afirst embodiment of an apparatus for counterbalancing weight;

[0015]FIG. 2 is a longitudinal cross sectional view of anotherembodiment of an apparatus for counterbalancing weight;

[0016]FIG. 3 is a cross sectional view along the line I-I of FIG. 2;

[0017]FIG. 4 is a perspective view of the apparatus shown in FIGS. 2 and3 and comprising a gear belt and lateral angular supports; and

[0018]FIG. 5 illustrates the apparatus shown in FIG. 4 disposed on apartially indicated headstock of a vertical machining centre.

[0019] The apparatus schematically shown in FIG. 1 for counterbalancingthe weight of a movable machine part of a machine tool comprises ahelical spring 1 of a helically wound spring steel ligament the innerend 2 of which is attached to an axis 6 turnably borne in two lateralcomponents 3 and 4 of a stationary support element 5 and the outer 7 endof which is attached to a fixed connection bridge 8 between the twolateral components 3 and 4 of the support element 5. On the two ends ofthe axis 6 turnably held in the two lateral components 3 and 4 bycorresponding bearings 9, which ends laterally protrude over the lateralcomponents 3 and 4, a roller 10 or 11 is mounted, respectively, so asnot to be turnable. The upper end portions of two ropes 13 and 14 fixedto a machine part 12 are attached to and guided by the rollers 10, 11 soas to be wound up and unwound when the machine part 12 is lifted orlowered. With a corresponding biasing of the helical spring 1 thus theweight force of the machine part 12 to be moved can be totally or partlycompensated by the spring force. In this way the driving power of afeeding drive required for lifting the machine part 12 can be clearlyreduced, and smaller dimensioned driving motors will be sufficient forthe feeding drive.

[0020] In FIGS. 2 to 5 an actual embodiment of an apparatus for weightcounterbalancing according to the invention attached to a verticallyshiftable headstock of a vertical machining centre is shown. In thisembodiment four helical springs 15 to 18 consisting of a spring steelligament having a rectangular cross section are arranged around an axis19 within a housing 20. According to FIG. 2 the housing 20 contains adrum 21 concentric to the axis 19 and two end side bearing covers 22 and23 by which the housing 20 is turnably held on the axis 19 by means ofbearings 24 and 25. The individual helical springs 15 to 18 areseparated from each other by spacer disks 26 for preventing friction orother mutual interference. The housing 20 with the bearings 24 and 25 isfixed in the axial direction by a shoulder 27 on the one side of theaxis 19 and an end disk 28 attachable to the other side of the axis 19.In another embodiment, however, the housing may be fixed as well and theaxis may formed so as to be turnable as shown in the principleillustration of FIG. 1.

[0021] As can be seen from FIG. 3 the inner end 29 of each spring 15 to18 is fixed to the axis via a lateral slit 30. The outer end 31 of thesprings 15 to 18 is bent around a rod 32 for an attachment to the drum21, said rod extending in the axial direction of the axis 19 in acorresponding recess in the drum 21. In addition, a clamping strip 33for fixing a gear belt 34 shown in FIG. 4 is screwed to the outer sideof the drum 21, the drum 21 of the turnable housing 20 being connectedto a headstock 35 only partly shown in FIG. 5 and shiftable along thevertical axis by a feeding drive (not shown) by said gear belt 24.

[0022] According to FIGS. 4 and 5 the axis 19 is held in forwardprotruding support parts 36 and 37 of two angular supports 38 and 39 soas to be secured against a rotation. The apparatus for counterbalancingweight is attachable to a stationary part of the machine tool via thetwo angular supports 38 and 39. On one end of the axis 19 a flange 40particularly visible in FIG. 2 and having radial bores 41 for adjustinga biasing of the helical springs 15 to 18 is provided. For maintainingan adjusted biasing, the axis 19 can be fixed in a certain angularposition, for example with respect to the support part 37, via lateralfixing screws (not shown).

[0023] With the embodiment of an apparatus according to the inventiondescribed above and shown in the drawing the weight of, for example, amachining unit shiftable along the vertical axis, can becounterbalanced. However, the invention is not limited to thisembodiment but can also be applied to counterbalancing the weight ofother vertically or transversely shiftable machine parts.

1. Apparatus for counterbalancing the weight of movable machine parts amachine tool, characterised in that the apparatus comprises one or morehelical springs (1; 15 to 18) the one end (7; 29) of which is connectedto a stationary component (8; 19) and the other end (2; 31) of which isconnected to the movable machine part (12; 35) for generating acounter-force counteracting the weight force of the movable machine part(12; 35).
 2. Apparatus according to claim 1, characterised in that theapparatus comprises a plurality of parallelly connected helical springs(15 to 18) the inner end (29) of which is attached to an axis (19) andthe outer end (31) of which is attached to a housing (20) which isconcentric with respect to the axis (19).
 3. Apparatus according toclaim 2, characterised in that the axis (19) is fixed and the housing(20) is rotatable.
 4. Apparatus according claim 2, characterised in thatthe housing (20) is fixed and the axis (19) is rotatable.
 5. Apparatusaccording to one of the claims 1 to 3, characterised in that the housing(20) is connected to the movable machine part (35) via a gear belt (34).6. Apparatus according to one of the claims 1 to 5, characterised inthat the helical springs (15 to 18) are arranged adjacent to each otherand spaced apart by spacer disks (26).
 7. Apparatus according to one ofthe preceding claims, characterised in that the helical spring (1) orthe helical springs (15 to 18) consist of a spring steel ligament havinga rectangular cross section.
 8. Apparatus according to one of thepreceding claims, characterised in that means (40, 41) are provided forbiasing the helical spring (1) or the helical springs (15 to 18). 9.Apparatus according to claim 8, characterised in that the means (40, 41)for biasing the helical springs (15 to 18) comprise an adjustment flange(40) provided on the axis (19) and capable of being fixed inpredetermined angular positions.